What was found
A TURBO HEAT BLANKET WAS INSTALLED ON 1-28-99. SUBMITTER STATED DURING THE INSTALLATION OF THE TURBO HEAT BLANKET, THE MECHANIC FAILED TO REINSTALL THE EXHAUST BYPASS VALVE PIPE (STC SA4731 NM/STC 4731 NM) THAT DIRECTED EXHAUST GAS OUTBOARD OF THE ENGINE. THE MISSING PIPE ALLOWED EXHAUST GASSES TO BLOW DIRECTLY ONTO THE ELECTRICAL WIRE BUNDLE FOR THE LANDING GEAR SWITCHES. THE EXTREME HEAT MELTED THE WIRE BUNDLE'S INSTALLATION AND SPARKED A FIRE SENDING SMOKE AND FUMES INTO THE COCKPIT COMPARTMENT CUTTING ALL ELECTRICAL POWER TO THE LANDING GEAR.